Concentration of phosphate ores



Dec. 8, 1953 J. B. DUKE ETAL 2,561,842

CONCENTRATION OF PHOSPHATE ORES Filed Aug. 3. 1950 Phas ha/e OreFeea Negalivefan reagen is, such as Caustic soda, fat/y acid and fuel 0/'/ CO/VO/T/O/W/VG ROUGHER PLOT/Z1 r/a/v S/h'ciaus Machlne-0ischarge 70 Waste iii/W050 FLOT/IT/O/V Phasphafe Concenfra ta /1 c/du/a/ed (2) Fralh Product F/OTO 770/7 Wafer M/adh'ng Mach/he Discharge Mineral acid, such as su/fur/c acid AG/TAT/O/V Wafer pen! reagen/qs/imas and wafer to waste Positive-Mn reagents, such as the higher a/Aohaf/c amines, etc.

FLOTA T/O/V MachMefl/scharge j Si/ia/ous From-Product (4) Phospha/e Concentrate I0 was/e F /na/ H/gh-graae Phospha/e Concenfra/e INVENTORS. JAMES B. DUKE WESLEY/V. HOUSTON A TTOR/VEYS Patented Dec. 8, 1953 UNITED STATES PATENT OFFICE 2,661,842 CONCENTRATION OF PHOSPHATE oREs James B. Duke, Medulla, and Wesley M. Houston,

Lakeland, Fla, assignors to Attapulgus Minerals & Chemicals Corporation; acorporation of Maryland Application August 3, 1950, Serial o, 177,374

4 Claims; 1

The pre n ihvntim elat'esto the oncen ation, of phosphate minerals from their ores, and" ay be regarded as improvement u o he method covered by the patent to Arthur Crago 2,293,640, issued August 13, 1942, now owne by the assignee of thepresent'application.

That Crago patent describes a method of con centrating phosphate mineral from. their ores;

whichrcomprises. (in the first step) subjecting the ore in an aqueous pulp to a. concentrating operation with means/awn reagents to separate a rougher concentrate of the phosphate values admixed with entrained. silicious gangue; treating the said rougher phosphate concentrate (in the second'step) with a mineral acid to remove the effect, on both the phosphate and silica particles, of the negative-don reagents used in the production of said. rougher concentrate; and then (in the third step) subjecting the thus acidtreated rougher concentrate in an aqueous-pulpto a concentrating operation witha positive-ion reagent which is a selective collector for thegangue in' said: rougher phosphate: concentrate to separate from it a collected material largely composed of thesilicious gangue, thereby 'produc'- ing a final phosphate concentrate;

The general object" of the present invention is to improve the method described ini said Crajgo patent so as to reduce the plant equipment required, and to-economize'in the quantityof positive-ion reagent employed, while still obtaining from the ore a phosphate concentrate having a low insoluble content and containing most of the phosphate in the ore.

These objects are attained by themethodof the. present invention which will be pnderstood from the ol o ,qescrip m taken in connection with the accompanying drawing showing a simplified. generalfiflow-sheet of atypical plant practicing the said method. It-will be understood thatthis fiow-sheetmerely contributesto an understanding of the invention, and that various modifications in the apparatus may be resorted to without departing from the spirit of-the invention as defl hed in the claims liereto' appended;

the flow-sheet drawing the" four stepsof the improved metho d are separatedby lines and are-marked 'l; 2, sand}?- Theiirstistep' I results in obtaining from the" phosphate ore feed, by the use of negative-ion reagents (as in etm o t .Crae P ten a ou her ho phate concentratei The ,S'ec'ond' step zflinvolves ul lie t nasa imueher. n nt atei ai u ous CTl honed 1hsaid or er. i hosphateconcentrate has:

either of the ways mentioned, it .is fed in a'n thereby removing as a part of the final product a froth-product having a low insoluble content, and a middling residue which contains mostof the silici'ous gangue and a considerable proportion of the phosphatein the rougher phosphate concentrate'i In the third step 3 of the method, saidmiddl'ing is treated with a mineral acid and rinsed to remove the'effect ofthe negative-ion: reagents on the particles in the middling. In the fourth and last step- 4 the thus acid treate'dmid -d ling is subjected to a' concentrating operation be used in the first step cf the method, ma es amples of positive-ion reagent's which may be used in the fourthstepfo'f the method are men-= patent- The mineral acid ph h acid, ineral a as such" g mme-acid;

use )I ne fth ifi teeb l have been found o area-harry satisfactory, ut t er term of ap m b m loyed;

ng th-ricen atingflopera'tions' The meaning of" retarded fiotation" second stepof the method illustrated V f etd aw nei nOW As illustrated, to the-r0 ugl erjphosphateSheen-- ate fise li e the th t p be he met-110ais a dedfaci'dulat ed fifotati H S bet? E9 acid'ulated flbt'atibn wa r having'a' low pff'jKW have found that it is possibleto'obtain the' sa e result by subjecting the rqugher phosphate concentrate to agitation and scrubbing with ordinary" (neutral? fiotatioriwater; Afterltherou'ghagueous pulp to iiotati'on cells i'n which-the pulp, owing to either of the prev-ious treatments men insoluble content-) which is added n; t ir sweet 6 d pweve using" I beem treated ..in.

phate concentrate may be subjected to retardedflotation treatment (in the second step of the method) by subjecting it to froth-flotation treatment in flotation cells in which the level of the pulp is maintained so low that only the top portion of the froth-product is removed. This froth-product is a high grade phosphate concentrate (having a low insoluble content); and the machine discharge from these cells, containing almost all of the silicious gangue and a. consid.

erable part of the coarser phosphate in the rougher phosphate concentrate, is the middling treated in the third and fourth steps of the method.

It will be apparent, therefore, that the second step of the method results in obtaining, by the retarded-flotation treatment of the rougher phosphate concentrate, by treatments which restrain the normal floatability of the rougher phosphate concentrate, a cleaner concentrate containing very little silicious gangue, and a middling containing the remainder of the coarser phosphate and most of the gangue in the rougher phosphate concentrate. The method which is the present invention, therefore, does not require the acid-treating (in the third step) and the flotation treatment with positive-ion reagents (in the fourth step) of all of the rougher phosphate concentrate, but merely the treating (in the third and fourth steps) of a much less Weight of material than is the case in the second and third steps of the method of the Crago patent. The advantageous result is that the method of the present invention requires the use of less acid (in the third step) and the use of less positiveion reagents (in the fourth step) than in the method of the Crago patent. The economy thus achieved in the use of positive-ion reagents was surprising and unpredictable, because the amount of silicious material floated in the last step of applicants method is obviously substantially the same as the amount of such material floated in the last step of the Crago method. Moreover, since less weight of material is treated in the third and fourth steps of the present method than in the second and third steps of the method of the Crago patent, the plant equipment requiredisreduced.

To contribute to a'clear understanding of the method which is the present invention, examples based on tests will now be described.

In each of the examples hereinafter described, the flotation feeds were composed of mesh deslimed particles of bone phosphate of lime (B. P. L.) and silica sand.

Example I -This example illustrates thexuse of weakly,- acid flotation water in the second step of the method. 7

A -35 mesh deslimed phosphate ore feed was conditioned in an aqueous pulp for 2 minutes at 70% solid with 0.5 pound of caustic soda, 3.0 pounds of fuel oil, and 0.37 pound of tall oil, all in pounds per ton of dry feed. The conditioned feed was diluted with tap water to about 20% solids in a minerals separation laboratory airnow flotation machine, agitated and aerated to produce a sand tailing in the machine-discharge 4 and a froth-product which was a rougher phos-' phate concentrate containing entrained sand particles.

The rougher phosphate concentrate was dewatered and repulped in the flotation machine at about 10% solid with water to which sufficient sulfuric acid had been added to produce a pH of 3, employing approximately 3.0 pounds .of H2804 per ton of original feed. The rougher concentrate was agitated briefly and then aerated and refloated in this acid water producing a retarded-flotation of a high-grade cleaner phosphate concentrate containing a minimum sand 7 content and a phosphate-rich middling machinedischarge consisting of both phosphate and sand particles. I

The said rich middling was agitated for about 3 minutesat approximately 50% solids with 0.75 pound of sulfuric acid per ton of original feed, and was then washed and rinsed free of acid and. spent negative-ion reagents. The acidtreated and rinsed middling was repulped in a flotation machine, conditioned for about 15 seconds with .025 pound of Armac T (tallow amine acetate made by Armour 8; Company), 0.1 pound of kerosene and 0.02 pound of pine oil frother (all in pounds per ton of original feed), and then was aerated and a low-grade silicious frothproduct was removed and sent to waste, leaving a high-grade phosphate concentrate in the machine-discharge which was combined with the high-grade phosphate concentrate produced by the second step. The metallurgical results of this test are recorded in the following table:

ROUGHER PHOSPHATE FLOTATION Percent Percent Percent Percent Products weight B. P. L msol. recovery 1. Feed 100. 0 2. R;)u%lfier clonctentratc 26 8 100.0

ro -pro uc 36.5 7 3. Silicious machine-dis- 0 0 95.3 charge to waste 63.5 2.0 4. 7

RETARDED CLEANER FLOTATION 4. Pliostplhategoncentrate ro -pro uct 22. 6 .2 5.-Middhng machine-dis- 77 2 6 65' 1 charge 13. 9 58. 2 30. 2

SAND FLOTATION FROM MIDDLING 6. Siliciousgroth-product 0 we e 3.9 7.'Machi13e-discharge 12 5 0 L8 I phosphate concentrate.. 10.0 76. 0 3.9 28. 4

OVERALL RESULTS 8."1vta% iliosplliiage conra e an 32.6 76.8 3. 9. Total tailing (3 and 6). 67.4 2.6 3-

Example II Thi example illustrates the use of neutral flotat1onwater and agitative scrubbing of the rougher concentrate in the second step of the.

method.

.A aaa'mesh deelimed conditioned in an aqueous pulp in the same.- man. her-and with the some quantities of negativeeion reagents, caustic soda ai'ld fueloil and tall oil, described in Example I, after which a. rougher phosphate. colleeiitiat Wag removed as a flotation frotmproduet, leaving a 'silicious machine d-is; oharge which was sent to waste- A The. rougher phosphate conceiitrat was then subjected, (in the eeeam te'p) to an agitativ sembbii ig action. iii a. paddleetype agitator for 3 mifiutes at approximately 50% solids with heir-,- tr'al tap-water and then repulped in the flotation niachliie with neutral tap water at about 1.0 Solids. The agitated rougher concentrate was then aerated; and refloated in neutral. tap water W thout the addition. of any. 9 mqdifying agents). thereby reeultingin a retarded cleaner flotation which. produced a high-grade hoenhate concentrate containing a low sand content, and a; middlin mechineedischaree consisting of bot phosphate and eand particles.

Ihesaid middling was then. agitated for about 3 minetee at; approximately 5.0% solids withv only 0531 pound H2594 and was then washed and rineecltre oi acid and spent negativeeion reag nts: The thus treat d middling was re: helped a flotation machine at about 10% sol s. condi ioned for 15 seconds with positive ion; m gen a consistin of only: -0.3; pound of Armac it llow am e ac a e), 0-1 pound. Q keroeeneand; 0.0-3; pound of; pine oil frother a hound he t or iginal iced), th n aerated. a d a s1; ions f oth-pro uct, was renew d and ten to wast leaving a i hrade, eheeizha e eo iceni i m the achin -dischar e. he ei tellmzeieal. tesultc ithieteetar recorded in the following table:

Ro-UG-HER PHOSPHATE FLO'IATION those reagents employed inl 40 s ts fh s. test hemmed. in the ollowin Percent Percent Percent t 7' V I Product s: g-pq- 3 1 .B.P.L.. 3

g recovery v I I V ROUGHER PHOSPHATE- FLO IATION gi e l e a.-.-.Y- f 100-;0 100:0 H M vim; "I l 0111? eolmenr f 45 'Percent fPercent 'Percent "9" r th-pr duct- 36 0 .942 PIQQQQ :3; T B?- :u 3- ymq busmaqhme 1 l. weight 3. P. L msol. recovery chargeto Waste 64 .0 5:8" w r 1, 1c0.0 27.2 100:0

RETARDED-CLEANER FLOTMFION- 2. R mer n t a 1 'oth v' du tgi le 9.3-2. 50 3. Silicious machine 4 41.1311 photo conce trate 7 charge to waste 65;9 2.8 1 6.8 5 ia glh-produml:lt .;a 29.6; 76,5 1 85,5 v

. ma e 18: p l

MLha:g5..I ?J% Q --Z at I 36.1 i 8.7 R TARDED-GEEANER E LQ'EATI'ON SAND FLOTAIION FROM MIDDIQINJG 5 Phosphaiteconcentmw V froth-lproduchufl fl, 22.7. 76.7 3.1 6&0. 5. Mi'ddl' fg'uiachine-dis fil'silic oua irothmrod charge 11.4 69.8 29.2 uct 3.9 1Q.& flown... 1.,6: 1 7 Machine d i v 'phqegli SAND FLOTAIION-ER-OMMIDDILING te 2,5 76.; 3,0 l .i I

6:siliclousfroth-product- I V i .l' J Y BALLRESULTS W t -r-w a; 16.2-

09: 7. Machine-diseha e" phosphate 'co11'cen-" i, 8; Total'phosphateeom trateeunu H. .H. 5 9.,9 78 Q l.'9,,. 28,11 9 'ctanltit'atfi l a'laid-Qiaih 76; 3:3- L 92.7

t cam! .a m

* 2;; Z3 v 65 ovtRatLeEscLrs Theexcellent r-a results offiihis xamp afTbtal phosphateconr. W ae-to both gradeandrecovery;and'the economy" 9 g i i w 1 1 731 2:7- initheam'ounts ofaci'dand'positive-ion reagents a almg' an I employed-' in comparison with thea'mounts of' practicing the method ofithe Crago patent, are obvious. Eqcqmzplfii ll I I ihieeexaniple illustrates; the praeticing or the phosphate on feed was 1 ton of original feed l then aerated;

e ec s-43;:

6. method by keepin'gthe' pulp level in the cleanerflotation cells Well below the froth lip: and each dling elf only the top part of the. froth; the second step of the method.

A mesh deslimed phospha e oif' ied eoiiditioneid with negative-ion. reagents iii an aqu uspulfi, diluted, and a rou h r.- phosphate concentratewa$ removed. as a fl ation i fe h'r product. in the ma'nher decribd iihxam les and 2, except that the negative-ion reagent quantities used were 0.35 pound: of caustic soda, 2.20 pounds of fuel oil and 021 pound of tall oil, all in po n per t n. f dry f ed.

In the second step, the rougher phosphate con; centrate was. then repulhed; in the flotation cell with tap water at about 0%v o d nd su jected' to retarded ii-otati nw i h w s chiev d by holdingthe pulp levelw l b low the froth l p of the cell and paddli off lythe topipart fora period of only 15 seconds- (about one-third of the complete normal flotation time.) thus producing a phosphate concentrate eonaining a i imum sand; c t and a; middling machine-discharge;consisting of both phosphate and: sand part cles..

he sa d m dd g wasag tate o 3 minutes at approx mately l-7Q So ids thlpou d of H289 d. t e ashed amt rins d t e of acid d spe t ne ative ion; r ag ts The. derailed; an i s d; mid ing reeu pedinthe flotation mac ne. t. ab t. Q% eol dsl; c nditioned t r 5. s on s w th n y -0 u d A mac (tallow amine acetate-),;, 012; pound of; kerosene-,. and 0.06, pound of pine, oil- (all inpounds per and. a low rade iliciou froth procluc was r moved, and sent to waste, leavinga h h-grade phosphate concentrate in the maehineedischarge which was: combinedv with the phosphate concentrate pro uce nhe c n the ti j considerable; ane-3 age teused in t The metallurgical reaccuses bal-impediments to the. flotation of the-phosphate concentrate in the second step, by maintaining low flotation-cell pulp-levels, and by incomplete removal of the froth-product. Furthermore, this example illustrates the achieving of economy in the amounts of acid and positiveion reagents employed in steps-three and four, as compared with the far greater amounts of these reagents used in tests 4 and 5 of the Crago patent.

Various combinations of the procedures described for achieving retarded-flotation of phosphate in the second step have proved equally effective in producing a high-grade phosphate concentrate containing only a very small amount of sand; and a rich middling which was easily freed of negative-ion reagents, after which the sand was floated with a minimum of cationic collector reagent. For example, the procedures tried successfully have included agitation of the rougher concentrate (produced in the first step) followed by flotation in acid water, agitation with small amounts oiacid followed by retardedflotation in tap water. In general, the use of acid reduces the agitation required to produce the same retarded-flotation efiect. Tests in which the rougher phosphate concentrates were subjected to agitative scrubbing for various lengths of time have shown that the retardedflotation effect is proportional to the time of the agitation of the rougher concentrates. In general, the grade of the phosphate concentrate produced by retarded-flotation increases with the retarding efiect, as does also the weight of the middling produced in the second step.

It seems to be a fact that the middlings (produced in the second step) appear to have flotation properties different from those of normal middlings. The usual middling from a normal phosphate cleaner flotation can be recirculated to the feed continuously with only a moderate buildup in the circuit until a stable condition is established. However, the middling produced by retarded flotation treatment of the rougher concentrate which has been tested by recirculation to the feed, continued to build up indefinitely and did not show any tendency to reach an equilibrium.

Various mineral acids, mineral acid salts, and organic acids have been used in the flotation water to retard the flotation of the phosphate concentrate and produce the middling, in the second step. These have included, for example, nitric acid, hydrochloric acid, propionic acid, potassium bisulfate, hydrofluosilicic acid, acetic acid and stannic chloride, producing waters varying from 3.0 pH to 5.7 pH. In general, the retarding efiect on the flotation increases with the acidity of the flotation water.

The method of the present invention has been successfully tested with the use of a number of negative-ion collector reagents to produce the rougher phosphate concentrate which is then subjected to a retarded-flotation in the manner described. The negative-ion collector reagents tested include red oil (crude oleic acid), fish oil fatty acids, tall oil and tall oil soap, and the petroleum sulfonate commonly known as mahogany s'ulfonate.

The flotation of silicious gangue from the acidtreated and, rinsed middling (in the fourth step) has be n carried out with. different positive-ion collector reagents, such as, for example, Armac T (Armour 8: Company's tallow amine acetate) erminal. earn amin hvar vh pua n a Rosin Amine D Acetate (a Hercules Company product). 1 i

It is a peculiar fact that thepositive-ion reagent requirement for floating the silicious gangue from the acid-treated and rinsed mid-.- dling is only a fraction of that required to float the same amount of silicious g-angue from the acid-treated rougher concentrate in the process of the Crago patent. Obviously, to produce the same high-grade total concentrate the two processes' must remove the same amount of silicious gangue from the rougher phosphate concentrate. Comparison tests. have shown that the amine reagent requirement for floating this silicious gangue from the acid-treated and rinsed middling according to the present method, is only one-half, one-third or less of that required to float the same silicious gangue from the total acid-treated rougher concentrate according to the process of the Crago patent. It appears that in the present method the lesser amount of phosphate present in the middling produced by retarded-flotation treatment allows a decrease in the amount of positive-ion reagent required.

The improvement in the percentage recovery of phosphate achieved by the present invention, over the method of the Crago patent, is shown by comparison of the tests in the Crago patent and the examples in the present specification. ln Cragos tests 4 and 5, the recoveries are 79.2% and 87.5% respectively (see the tabulation on page 3 of the Crago patent). In the examples hereinbefore given, the over-all recoveries are 93.5%, 92.7% and 92.3% respectively. Since the amount or" phosphatic material treated in the Florida phosphate area alone runs into millions of tons annually, this improvement in over-all recovery is important.

The economy in the amount of positive-ion reagents resulting from the applicants method, in comparison with the method of the Crago patent, is also. important. In tests 4 and 5 reported on page 3 of the Crago patent, 0.20lb. of octa;

decylamine acetate were required. Whereas, in

Examples 1, 2 and 3 of the applicant's specifica-.

tion only .025 1b., .03 lb. and .06 lb. of amine acetate were used. Thus, it is apparent that the applicants method permits the use of very con.

siderably less positive-ion reagents than is required in the Crago method. Since positive-ion reagents are rather expensive, economy in the use of them is important. 7

Obviously, therefore, the applicants method is a valuable improvement on the method of the H Crago patent.

- What is claimed is:

l. A method of concentrating phosphate minerals from their ores which comprises the fol-,

lowing sequence of steps: (1) subjecting the ore in an aqueous pulp to a froth-flotation treatment with negative-ion reagents, thereby pro ducing a froth-product which is a rougher con-, centrate of the phosphate values mixed with some,

silicious gangue; (2) subjecting said rougher con centrate in an aqueous pulp to retarded frothflotation treatment and removing as a part of the final product a froth-product having a lowinsoluble. content, and a middlingresidue; (3) sub-; jecting said middling inan aqueous pulp to treat-.: I mentwith a mineral acid followed by rinsing withwater, thereby removing from said middling sub-,

stantially all of said negative-ion reagents; and (4) subjecting said acid-treated and rinsed middling in an aqueous pulp to a froth-flotation treatment with positiveeion reagents thereby.pro-

ducing a froth-product mostly composed of silicious gangue which is discarded, and a residue which is a high-grade phosphate concentrate and can be combined with the previously mentioned commercial-grade phosphate concentrate; thereby producing a final high-grade phosphate concentrate containing a high proportion of the phosphate in the ore.

2. The method of concentrating phosphate minerals according to claim 1, using a weaklyacid flotation water in the retarded froth-flotation treatment in the second step (2).

3. The method of concentrating "phosphate minerals according to claim 1, using neutral fiotation water and agitative scrubbing of the rougher phosphate concentrate in a thick pulp as a part of the retarded froth-flotation treatment in the second step (2) 4. The method of concentrating phosphate minerals according to claim 1, in which in the References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,480,884 Dolbear Jan. 15, 1924 2,293,640 Crago Aug. 18, 1842 2,350,943 Thompson et a1 June 6, 1944 2,461,813 Duke Feb. 15, 1949 OTHER REFERENCES Milling Methods for 1934, published by the A. I. M. M E., New York, New York, 1935, pages 452 and 460 (copy in Div. 25).

Taggart, Handbook of Mineral Dressing,

0 1945, Section 12, page 100 (copy in Div. 25). 

1. A METHOD OF CONCENTRATING PHOSPHATE MINERALS FROM THEIR ORES WHICH COMPRISES THE FOLLOWING SEQUENCE OF STEPS: (1) SUBJECTING THE ORE IN AN AQUEOUS PULP TO A FORTH-FLOTATION TREATMENT WITH NEGATIVE-ION REAGENTS, THEREBY PRODUCING A FROTH-PRODUCT WHICH IS A ROUGHER CONCENTRATE OF THE PHOSPHATE VALUES MIXED WITH SOME SILICIOUS GANGUE; (2) SUBJECTING SAID ROUGHER CONCENTRATE IN AN AQUEOUS PULP TO RETARDED FROTHFLOTATION TREATMENT AND REMOVING AS A PART OF THE FINAL PRODUCT A FROTH-PRODUCT HAVING A LOW INSOLUBLE CONTENT, AND A MIDDLING RESIDUE; (3) SUBJECTING SAID MIDDLING IN AN AQUEOUS PULP TO TREATMENT WITH A MINERAL ACID FOLLOWED BY RISING WITH WATER, THEREBY REMOVING FROM SAID MIDDLING SUBSTANTIALLY ALL OF SAID NEGATIVE-ION REAGENTS; MID(4) SUBJECTING SAID ACID-TREATED AND RINSED MIDDLING IN AN AQUEOUS PULP TO A FROTH-FLOTATION TREATMENT WITH POSITIVE-ION REAGENTS THEREBY PRODUCING A FROTH-PRODUCT MOSTLY COMPOSED OF SILICI OUS GANGUE WHICH IS DISCARDED, AND A RESIDUE WHICH IS A HIGH-GRADDE PHOSPHATE CONCENTRATE AND CAN BE COMBINED WITH THE PREVIOUSLY MENTIONED COMMERCIAL-GRADE PHOSPHATE CONCENTRATE; THEREBY PRODUCING A FINAL HIGH-GRADE PHOSPHATE CONCENTRATE CONTAINING A HIGH PROPORTION OF THE PHOSPHATE IN THE ORE. 